This invention relates to an electro-optic inspection system of transparent or semitransparent containers, such as glass and plastic bottles to be used as beer bottles, alcoholic drink bottles and so on, for the presence of contaminants and hazardous materials.
New bottles require inspection because of potential defects that form hazardous glass structures within the bottles, whereas bottles that are recovered from consumers and have been cleaned for re-use, require an inspection for liquid and solid contaminant materials. Reject bottles must be discriminated from the clean or flawless bottles because of their potential physical or biological hazard to the consumer and to maintain the quality of the products.
The detection of these internal glass defects (such as fragile glass filaments that can break off during the filling operation) and contaminants is not a simple task. The conventional use of human visual inspectors is subject to a wide range of human limitations such as establishing and maintaining an inspection baseline or reference and loss of detection reliability and sensitivity from human factors such as fatigue. Systems which employ the transmission of localized optical radiation (small diameter optical beams) in their inspection principle are sensitive to the imprecise structure of the glass container. For example, bottles which are fabricated by blow molding will have a variation in wall thickness as well as mold seam markings and mold identification numerals. Many bottle designs include embossed regions on the outer surface of the glass to enhance the bottle's structural integrity. These variations in the bottle's structure produce an optically noisy background against which a small contaminant particle or structural defect must be detected. The interference effects of this background noise is enhanced in inspection concepts that use imaging systems or transmit small diameter beams (e.g., laser beams) through the walls or bottom of the glass container in performing the inspection task. For example, a small diameter beam transmitting through the container will be refracted and reflected (resulting in an attenuation of the transmitted light) from these localized bottle structures. With an inspection system using an imaging system, the depth of focus is usually large enough to include both the inner and outer wall surfaces. This physical background is then almost impossible to separate from a contaminant particle without desensitizing the inspection response. The inspection of glass containers is further complicated when a permanent label is present on the container wall. The label forms a uniform background, blocking or scattering optical transmission. As a result, a labeled area on a semitransparent container usually receives a less than satisfactory inspection for the presence of contaminants or hazardous materials.